Hydraulic brake



p 23, 1941- G. E. MARTIN v 2,256,721-

HYDRAULIC BRAKE Filed Oct. '9, 1959 3nventor Patented Sept. 23, 1941 HYDRAULIC BRAKE George E. Martin, Detroit, Mich., assignmto en. eral Motors Corporation, Detroit, Mich, a corporation ofDelaw are Application October 9, 1939, Serial No. 298,569

4' Claims. (Cl. 188-108) This invention relates to brakes and more particularly to brakes wherein opposed shoes are spread into frictional engagement with the drum by either one or both of two applying means, one of which employs a hydraulic motor.

An object of the invention is to modify the conventional hydraulic motor in such a way that air may not be drawn into the cylinder of the mo.- tnr when the shoes are spread solely by the other applying means.

Other objects and advantages will be understood from the following description. I The invention is illustrated by the accompanying drawing in which:

Figure 1 is a section through a brake' drum and wheel cylinder showing the improvements emanchor pin I! carried by plate i through a link l9. the links being pivoted to the shoes as at 2!. Numeral 23 is a diagrammatic representation of a conventional expedient for holding the shoe toward a fixed cover plate 25 and away from the rotatingdrum.

In motor vehicles wherein the shoes are spread by hydraulic applying means there is provided between the pair of shoe ends remote from the anchored ends, a hydraulic motor or wheel cylinder. Such a cylinder is shown at 21. In the case of four wheel-brakes there will be one such cylinder for each brake. The cylinder has two pistons 29, 29' between which are seals 3|. Between the seals is a spring 33 operable to hold the seals against the pistons. In the embodiment shown, the pistons are hollow cups. Fluid from a suitable master cylinder is forced into the space between the pistons through an inlet opening 35. The incoming fluid moves the pistons outwardly away irom eachother. To vent air from the cylinder there is an opening marked 31, the

opening being normally closed by a plug not shown. 1 v

The connection between each piston and the adjacent shoe comprises a cup-shaped disk 4| having an annular portion embracing and slid- I terminally secured to the shoes to determine their position of release by the engagement of. disks 4| with the end walls of the cylinder. Adjustment of the released position is made by rotating the nut 43 to reciprocate the plunger 45 relative to the piston 29.. To hold the parts in ad- Justed position a spring member 49 is secured intermediate its ends to the cylinder at 39, the ends being'adapted to enter notches 5| formed in the cup With such a brake assembly it is customary, especially in the case of rear wheels, to add mechanical shoe spreading linkage operable independently of the hydraulic applying means by an emergency lever. This supplementary brake applying mechanism is available for emergency op eration and for holding the car when parked.

On the drawing is shown a lever 53 pivoted to shoe 9 at 55. Lever 53 has a hooked end-51 to which is attached a suitable tension link or cable 59. This cable is to be connected with an emergency lever not shown. The cable 59 is preferably carried in a. flexible housing 89. A spring 62 j is used as shown to normally hold the mechanical applying means in brake release position; The applying means is completed by means of a link 6i engag'ingat 63 an intermediate point oi lever 53 and pivoted to shoe I at 95. that a pull on cable 59 operates through the lever 53 and link 6! to spread the shoes into contact with the drum. The two spreading means may obviously be used separately or together.

At this point it should be explained that when the brakes are released there is a certain residual fluid pressure within the cylinder 21 and between the pistons, the master cylinder being usually provided with a spring loaded valve for this purpose. This residual pressure obviously tends to push the pistons apart. Spring 33 supplements this residual pressure. Spring 41 is of such strength as to overcome the spreading action of the residual pressure and the spring 33. When to the potential energy of the residual pressure and the spring 33 is added the manually ap-' plied force acting through the fluid column the tension of spring 41 is overcome and the pistons move outwardly and force the shoes into trio-- tional engagement with the drum. 11', instead of the pressing pedal the operator spreads the shoes adapted to engage the end 01! the cy1inder'and through the instrumentality-of parts 53 and 6|.

It will be seen I 2 1 spring 41 is no longer-eii'ective to overcome the residual pressure and the tension of spring 33.

In the absence of any means to prevent it, each piston would then move outwardly and reduce 1 the action of the residual pressure, and means to retain said piston from movement under the influence of said residual pressure and second spring I,

when the mechanical applying means is operated independently and the first spring means thereby rendered inoperative to overcome said residual pressure and second spring, said last named means comprising a spring actuated detent en- 1 the residual pressure. The reduction in pressure gaging said piston.

might be sufiicient to .cause a fiow of air around 2.. In a brake, hydraulic applying means, methe pistons and the seals into the space between chanical applying means, said two means adapted 1 the pistons. This is decidedly disadvantageous to be operated independently, said hydraulic. because the most eflicient action of a hydraulic means including a cylinder, a piston therein subj brake requires that the system be filled with a l0 ject to fluid pressure to apply the brake and subnon compressible medium. To prevent this pisject to residual fluid pressure when the brake is 1 ton movement and the entry of air, as above de- 1 released, first spring means to overcome said 1 scribed, there is added, in accordance with this residual pressure and holding the brake released, invention, a spring detent device which holds the a second spring in said cylinder supplementing. 3 pistons in their retracted position against the the action of the residual pressure, and means to pressure of the residual fluid and the spring 33 retain said piston from movement under the inwhen the influence of spring ll is removed by the fluence of said residual pressure and second operation of the mechanical applying means. In spring when the mechanical applying means is Figure 1 a fiat spring 67 is secured to the cylinoperated independently. and the first spring der adjacent its middle point by screws 89. Each means thereby rendered inoperative to overcome end of the spring engages a detent "H which exsaid residual pressure and second spring, said. tends through the cylinder wall and ismovable in last named means comprising a detent slidable j a slot 13 in the piston. Normally and with the through the wall of said cylinder, and yielding j piston in its retracted position the detent is in means on the outer wall of said cylinder adapted the inner end 01' h The Pressure f prin to project the detent through the cylinder wall 1 61 is such as to equal or slightly exceed the comand into the path of movement of said piston. bined pressure of the,residual fluid and the spring 3. In a brake, hydraulic applying means, me- 33. When the brake is applied hydraulically the chanical applying means, said two means adapted f pressure of spring 61 is easily overcome. When to operate independently, said hydraulic means the brake is applied mechanically, spring 61 holds 3@ including a cylinder, a piston therein subject to the piston in its inner position as they shoes fluid pressure to apply the brake and subject to spread to operative position. The residual presresidual fluid pressure when thebrake is released, sure remains unchanged and no air can enter spring means to overcome said residual pressure the space between the pistons. and hold the brake released, and means to retain 1 In the modification shown by Figure 2 the pissaid piston from movement under influence of 3 ton 30 is shorter in length and the detent H ensaid residual pressure when the mechanical apgages the end wall of the piston instead of the plying means is operated independently and the inner end of a slot formed therein. The Operaspringmeans is thereby rendered inoperative to 1 tion is the same as described in connection with overcome said residual pressure, said last named j Figure 1 40 means comprising a spring actuated detent en- 1 claim; 0 gaging said piston. 1. In a brake, hydraulic applying means, me- 4. In a brake, hydraulic applying means inl chanical applying means, said two means adapteluding a movable part, resilient means operable ed to be operated independently, said hydraulic against the hydraulic applying means to release "means including a cylinder, 9. piston therein subthe brake, said applying means being subject to 1 ject to fluid pressure to apply the brake and residual pressure when the brake is released, v subject to residual fluid pressure when the brake other means to apply the brake against the action is released, first spring means to overcome said of said resilient means and yieldable detent residual pressure and holding the brake released, means operably engaging a d a P t to a second spring in said cylinder supplementing hold the same from brake applying movement under the influence of said residual pressure when said other means is used to apply the brake.

GEORGE E. MARTIN. I 

